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Is the 5:2 Diet Busted?

The pundits are all over the 5:2 diet (one of the more famous versions of an intermittent fasting diet) because fasting, they say, can lower your immune system and lead to infections. Here’s a typical post:

“Intermittent Fasting or 5:2 diet” affects the nervous system and increases people’s vulnerability to infection, according to a University of Bath study.

These and many other stories seemed to feed off of each other and all come to similar conclusions, namely that intermittent fasting weakens the human immune system. But all of these articles are based on a study that didn’t have to do with humans and didn’t have to do with fasting.

The actual study, titled Hormesis Results in Trade-off with Immunity, is a study of flies conducted at the University of Bath. Hormesis describes the surprising extra fitness that results with low doses of certain stressors such as heat, fasting or toxins. In this study, the flies were coated with a dead fungal toxin that stressed them. The results showed that the treated flies lived longer and had more children. However, there was an interesting loss of immune function that left the flies more vulnerable to doses of live fungus. The authors of the study conclude:

It seems quite plausible that in healthy patients, we could employ our natural life-history responses to environmental cues [such as fasting — Ed.] to further improve their health. However, the consequences of hormetic treatments for infected patients could be dire.

How did the researchers connect fungus-coated flies to human fasting? Because a similar set of genes in both humans and flies seem to be involved in hormesis. So is this the death knell for the 5:2 diet or fasting in general? Hardly. But it indicates that some care should be taken before undertaking it. If you are at risk for infection, or if your immune system is already compromised, you might think twice. Especially if you’re a fly.

This following study regards men, and it have a sense. We know that 3-4 days of fasting regenerate the immune system. Researchers have seen that during fasting the count of lymphocyte decreases, and then increases rapidly when you go back to eating, “resetting” the immune system. So it’s logical that during the fasting period the body is more susceptible to infections. Perhaps it’s a coincidence, but from several month I fast regularly (600 kcal day) a couple of days at week, and during this period I took a small flu (with some fever) and an annoying sore throat. They were at least 13-15 years that I do not get sick.